Coaxial cable is used to transmit radio frequency (RF) signals in various applications, such as connecting radio transmitters and receivers with their antennas, computer network connections, and distributing cable television signals. Coaxial cable typically includes an inner conductor, an insulating layer surrounding the inner conductor, an outer conductor surrounding the insulating layer, and a protective jacket surrounding the outer conductor.
Each type of coaxial cable has a characteristic impedance which is the opposition to signal flow in the coaxial cable. The impedance of a coaxial cable depends on its dimensions and the materials used in its manufacture. For example, a coaxial cable can be tuned to a specific impedance by controlling the diameters of the inner and outer conductors and the dielectric constant of the insulating layer. All of the components of a coaxial system should have the same impedance in order to reduce internal reflections at connections between components. Such reflections increase signal loss and can result in the reflected signal reaching a receiver with a slight delay from the original.
Two sections of a coaxial cable in which it can be difficult to maintain a consistent impedance are the terminal sections on either end of the cable to which connectors are attached. For example, the attachment of some connectors requires the removal of a section of the insulating layer at the terminal end of the coaxial cable in order to insert a support structure of the connector between the inner conductor and the outer conductor. The support structure of the connector prevents the collapse of the outer conductor when the connector applies pressure to the outside of the outer conductor. Unfortunately, however, the dielectric constant of the support structure often differs from the dielectric constant of the insulating layer that the support structure replaces, which changes the impedance of the terminal ends of the coaxial cable. This change in the impedance at the terminal ends of the coaxial cable causes increased internal reflections, which result in increased signal loss.